Process and apparatus for etching an image within a solid article

ABSTRACT

An apparatus and process for etching an image within a solid article including the steps of focusing a laser to a focal point within the article and positioning the article with respect to the focal point. The laser is fired so that local disruption occurs within the article to form the image within the article.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of my U.S. patent application Ser. No.07/992,918, filed Dec. 18, 1992, and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and apparatus for etching animage within a solid article. More specifically, it relates to laseretching individual points of an image within the article to form theimage.

2. The Prior Art

It is known that laser light interacts with opaque materials to alterthe physical characteristics of the material. This phenomenon isutilized in various laser technologies, i.e., cutting, welding, drillingholes, and imprinting textures on the surface of materials. The U.S.patent to Sorkoram, U.S. Pat. No. 4,851,061, discloses a method andapparatus using a laser beam for cutting thermoplastic materials intodifferent shapes. The U.S. patent to Macken, U.S. Pat. No. 4,458,133,discloses a laser apparatus for cutting sheets of material usingtemplates.

Also known are materials which reflect laser light, for example, theU.S. patent to Nakamachi et al, U.S. Pat. No. 5,066,525, and the U.S.patent to Wood et al, U.S. Pat. No. 4,842,389, which discloseholographic heads-up displays. Also, it is known that laser beams travelthrough transparent materials, for example, lenses in laser systems,without interaction. However, if the concentration of laser radiationreaches a sufficiently high level, the transparent material may begin tobreak down, for example, when lenses in laser systems are damaged.Previous attempts have not been made to constructively utilize theinteraction of laser beams with transparent materials.

SUMMARY OF THE INVENTION

It is therefor an object of the present invention to provide a processand apparatus which overcomes the drawbacks of the prior art andutilizes a laser to constructively interact with a transparentmaterials.

It is another object of the present invention to provide a process andapparatus where a focused laser beam causes local destruction within asolid article, without effecting the surface thereof.

These and other related objects are achieved according to the inventionby a process for etching an image within a solid article, including thesteps of focusing a laser to a focal point within the article. Theposition of the article with respect to the focal point is varied andthe laser beam is fired so that local disruption occurs within thearticle to form the image within the article.

The apparatus for etching an image within a solid article includes alaser focused to a focal point within the article. The position of thearticle with respect to the focal point is varied. Control means,coupled to the laser, and positioning means are provided for firing thelaser so that a local disruption occurs within the article to form theimage within the article.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will become apparentfrom the following detailed description considered in connection withthe accompanying drawings which disclose several embodiments of thepresent invention. It should be understood, however, that the drawingsare designed for the purpose of illustration only and not as adefinition of the limits of the invention.

In the drawings, wherein similar reference characters denote similarelements throughout the several views:

FIG. 1 is a schematic view of the apparatus according to the invention;

FIG. 2 is a diagram of the article in which the image is etched;

FIG. 3 is a flow chart describing the process according to theinvention;

FIG. 4 is a diagram showing how the article is positioned;

FIG. 5 is an alternate embodiment of the positioning system from FIG. 4;and

FIG. 6 is a further embodiment of the positioning system shown in FIG.4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in detail to the drawings and, in particular, FIG. 1,there is shown an impulse laser 11 which projects a laser beam 12towards focusing lens 13. Beam 12 is then focused to a focal point 14within a solid article 15. A movable platform 16 supports and alters theposition of article 15. A controller 17 is coupled to impulse laser 11and movable platform 16 to coordinate their respective functions.Controller 17 instructs movable platform 16 to move article 15 so thatfocal point 14 is located at a particular point within article 15.Controller 17 then directs impulse laser 11 to generate a pulsed laserbeam 12 which, after passing through focusing lens 13, interacts withthe material of article 15 at focal point 14.

Article 15 may be made, for example, from clear glass, colored glass,optical crystals or organic glass, and may be translucent ortransparent. Glass is generally classified as an amorphous solid. In thecase of a transparent block of glass, the internal structure allowslight rays to pass directly through. The intensity of the radiation atfocal point 14 disturbs or locally destructs the glass in the vicinityof focal point 14. This is achieved, for example, by heating and/ormelting and/or expanding the glass at the focal point to cause cracking.The surface and surrounding area of the block of glass are unaffected.

This local destruction or disruption creates an imperfection withinarticle 15 which has a lower translucence than the surrounding areas. Asa result, the point of local destruction appears as a foreign objectencased within a glass block. The characteristics of the localdisruption, e.g., the size of the point, can be controlled by adjustingthe intensity or length of the laser emission. A series of localdisruptions can be coordinated to form two-dimensional andthree-dimensional images within solid articles. Surprisingly, it wasfound that the contrast of the image can be increased by introducinglaser beam 12 into a first side 18 of article 15 which is different froma second side 19 of article 15 which will ordinarily be facing theobserver, as shown in FIG. 2. The laser beam may enter the objectthrough first side 18 at an angle of 90° from the observation anglethrough second side 19, for example. The surface through which the beamenters is preferably an optically flat surface. The beam has a 90° angleof incidence, for example. If the beam had another angle of incidence,the beam would refract as it entered the dense material, complicatingthe calculations required to form the image from discrete points. Theimage is created by first melting the farthest points from first side 18and then melting the points closer to first side 18. In this manner, theincoming beam need not pass through already melted areas, which wouldcause distortion and/or refraction.

Laser 11 may be, for example, a hard body impulse laser, a pulsedsolid-state laser, or a Q-spoiled laser. The laser preferably has anenergy output of 50 Mjoules, a pulse frequency of 1 Hz and a pulselength of 10 nsec, for example. The characteristics of the laser shouldbe selected so that the laser emission disrupts, melts or causes amicro-fracture of the article at the focal point without affecting thearea surrounding the focal point. Lens 13 is a standard type, as is wellknown to those skilled in the art. Beam 12 enters lens 13 with the raysalong parallel lines and having the same frequency. The beam can befocused into a spot approximately as wide as the wavelength of the rays.Thus, intense energy can be focused into a very small area.

FIG. 3 shows a flow chart outlining the various steps for etching animage within a solid article. In initial step 30, the image coordinatesare loaded into controller 17. If a two-dimensional image is to beetched, a series of two-dimensional coordinates will be loaded intocontroller 17. If a three-dimensional image is to be etched, a set ofthree dimensional coordinates will be loaded into controller 17. Thecoordinates may represent the absolute position of each individual pointof the image, or they may represent the relative position of a pointwith respect to the previous point. For example, the cartesiancoordinates representing a two-dimensional letter "L" would be asfollows: (0,4) (0,3) (0,2) (0,1) (0,0) (1,0) (2,0). If the coordinateswere describing the relative position of one point with respect to theprevious point, the same two-dimensional letter "L" would be representedby the following coordinates: (0,4) (0,-1) (0,-1) (0,-1) (0,-1) (1,0)(1,0). The relative position coordinates are calculated by taking thedifference between consecutive coordinates. This calculation orconversion can be performed by controller 17 or may be performed aheadof time. The various coordinates may also be represented in other ways,e.g. vectors.

Next, in step 32, article 15 is mounted on movable platform 16 and theinitial position is calibrated. For example, it is important forcontroller 17 to recognize the edges and center of article 15. In thismanner, controller 17 can appropriately coordinate the operation ofmovable platform 16 and laser 11 so that the image is properly placed orcentered within article 15. If a set of image coordinates are centeredaround the origin (0,0), then it will be necessary for controller 17 totranslate the entire set of coordinates so that the image will becentered around the center point of article 15. Also, different sizedarticles 15 will have different center points. The coordinates can beappropriately adjusted by translating the coordinates so that theycenter around the central point of article 15 instead of the origin(0,0). This translation of coordinates can be performed by controller 17or can be calculated beforehand with the translated coordinates thenbeing loaded into controller 17.

It is also possible that controller 17 or a computer in a prior steprotates, enlarges, reduces, or otherwise manipulates the imagecoordinates so that one set of image coordinates could actually be usedto generate a variety of slightly different but related images withinarticle 15.

In step 34, the start sequence is initiated. In step 36, controller 17transmits the first coordinate to movable platform 16. In step 38,movable platform 16 moves to the coordinate as instructed by controller17 and then signals controller 17 that the location has been reached. Instep 40, controller 17 then triggers impulse laser 11 to fire. Localdisruption is then caused at focal point 14. In step 42, controller 17queries as to whether additional coordinates exist in the imagecoordinates file. If additional coordinates exist, step 44 is executedin which controller 17 transmits the next coordinate to movable platform16, following which steps 38, 40 and 42 are repeated. This sequencecontinues for all coordinates in the image file. If, in step 42,additional coordinates are not present in the image coordinate file,then step 46 is executed in which the sequence is terminated.

FIG. 4 shows a preferred embodiment with laser 11 and focusing lens 13in a fixed position. Movable platform 16 is capable of movement alongthree axes, designated as the "X", "Y" and "Z" axes. Movement in each ofthe three directions is controlled by a step motor or a pair of stepmotors, for example. However, any type of an XYZ table can be employedas is well known, for example, from U.S. Pat. Nos. 5,149,937 and5,153,409, the subject matter of which is incorporated herein. The stepmotors, for example, rotate threaded rods which pass throughcooperatively sized bolts. The bolts are fixed to movable platform 16such that rotation of the threaded rods causes movable platform 16 tomove a predetermined distance along one of the three axes. Each stepmotor rotates the threaded rod through a predetermined angle following asingle pulse. The predetermined angle may be 90° or 360°, for example.The angle may be adjusted through the use of a transmission. Therotation of the threaded rod moves the cooperatively sized bolt andplatform a short linear distance. Preferably, this linear distance is asufficiently small increment to allow the platform to move accurately toeach coordinate within a predetermined tolerance.

Controller 17 may include a microprocessor which signals one or morestep motors by one or more pulses to move movable platform 16 based onthe difference between consecutive coordinates. A sufficient number ofpulses are provided so that the increments of the step motors add up tothe required linear distance. Controller 17 moves platform 16 so thatfocal point 14 is moved to various positions within article 15 to createlocal disruptions and form an image or outline of an image. Focal point14 lies within a plane 21 which is transverse to the direction of travelof beam 12. The concentration of radiation of beam 12 in front of plane21 (direction 23) or in back of plane 21 (direction 22) is sufficientlylow to pass through article 15 without affecting it. Only at point 14within plane 21 does beam 12 reach a sufficiently high concentration tolocally disrupt the structure. On either side of plane 21, beam 12 formsa cone, as can be clearly seen in FIG. 1. In direction 23, the coneextends to lens 13. In direction 22, the cone extends outward toinfinity. The intensity of the laser emission, i.e., radiation isdistributed along the cross-sectional area of the beam. As can beappreciated, the smaller the area, the higher the concentration ofradiation. At plane 21, beam 12 has the smallest cross-sectional areaand the highest concentration of radiation. Certain areas of article 15in direction 22 or 23, although within beam 12, are unaffected by beam12.

In FIG. 5, movable platform 16 is capable of moving in two dimensions inthe "XY" plane. Platform 16 is moved in a manner similar to an XYplotter. Impulse laser 11 and focusing lens 13 are fixed with respect toeach other in housing 20. Housing 20 is mounted on laser movementcontroller 24 which moves housing 20 vertically in the "Z+" and "Z-"directions. Laser movement controller 24 and movable platform 16cooperatively provide three-dimensional movement of focal point 14relative to article 15. In this arrangement, controller 17 wouldtransmit the new "X" and "Y" coordinates to movable platform 16 and thenew "Z" coordinate to laser movement controller 24 to move focal point14 to the new location.

As can be seen in FIG. 6, article 15 is attached to movable platform 16which moves in the "X" direction, i.e., into and out of the page.Impulse laser 11 is fixed in position. Mirrors 25 and 26 direct laserbeam 12 from impulse laser 11 through focusing lens 13 to focal point14. Mirrors 25 and 26 and focusing lens 13 are located within a housing20. Housing 20 is capable of moving along the "Y" axis from the positionshown in solid line to the position shown in phantom line. Mirror 25 andlens 13 are maintained at a fixed distance from each other withinhousing 20. To alter the position of focal point 14 in the "Y" directiononly, housing 20 is moved in the "Y" direction with mirrors 25, 26 andlens 13 remaining fixed with respect to each other. Mirror 25 and lens13 can move together in the "Z" direction within housing 20. In order tomove focal point 14 in the "Z" direction, mirror 26 would remain fixedand mirror 25 and lens 13 would move in the "Z" direction.

In order to move focal point 14' to focal point 14", mirror 26 moves inthe "Y" direction (from the solid line position to the phantom lineposition), and mirror 25 and lens 13 would move in the "Z" direction(from the solid line position to the phantom line position). Article 15would move in the "X" direction, if required. It would also be possibleto have article 15 fixed and add a third mirror to housing 20 to providemovement of the beam in the "X" direction. In a case of three mirrors,each mirror would move along one axis parallel to the incident beam onthat mirror.

While only several embodiments of the present invention have been shownand described, it is to be understood that many changes andmodifications may be made thereunto without departing from the spiritand scope of the invention as defined in the appended claims.

What is claimed is:
 1. An apparatus for etching an image within a solidarticle, comprising:an impulse laser for generating a laser emissionhaving a power rating of 50 Mjoules and a pulse length of 10 nsec and apulse frequency of 1 Hertz; a focusing lens located at an operativedistance from said laser to focus the laser emission to a focal pointwithin the article; means for positioning the article with respect tothe focal point including (a) a motor driven support bench for receivingand supporting the article; (b) a threaded nut attached to said supportbench; and (c) at least one step motor including a threaded rodcooperatively sized to engage said threaded nut, whereby said at leastone step motor rotates said threaded rod to move said threaded nut andsaid support bench linearly along said threaded rod axis; control meanscoupled to said impulse laser and said positioning means for firing saidlaser so that a local disruption having a lower translucence than thearticle occurs at the focal point within the article, without affectingan area surrounding the focal point, to form the image within thearticle.